Any candle that closes above its open, usually drawn green or hollow.
A bullish candle simply means buyers finished the period ahead. It says nothing about the larger trend: a green candle inside a downtrend is often just a pause.
The useful detail is the combination of body and shadow. A green candle with a large candle-body and a tiny upper-shadow means buying pressure held right into the close. A green candle with a huge upper shadow means buyers won on points but were rejected at the highs, which is far less constructive.
Colour alone is one of the weakest signals on a chart. Every meaningful candle read involves size, location relative to a level, and context from the bars around it.
Original diagrams for the ideas on this page. Illustrative, not real market data.
The parts of a candlestick. One candle sums up a slice of time: the thick real body runs from the opening price to the closing price, and the thin wicks reach out to the highest and lowest prices traded. Colour tells you which way the body ran.
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